A blue light emitting diode element, for example, includes an InGaN semiconductor light emitting portion provided on a surface of a sapphire substrate, and electrodes respectively provided on P- and N-sides of the InGaN semiconductor light emitting portion (see Patent Document 1 listed below). However, it is necessary to provide the P-side and N-side electrodes on the InGaN semiconductor light emitting portion and route wires from the electrodes, because the sapphire substrate is insulative. Therefore, light from the InGaN semiconductor light emitting portion is blocked by the electrodes and the like, so that the light extraction efficiency is low.
This problem is alleviated by employing a flip-chip structure in which the InGaN semiconductor light emitting portion is bonded to a mounting board in opposed relation to extract the light from the side of the sapphire substrate (see Patent Document 2 listed below).
In the light emitting diode element of the flip-chip type, one surface of the sapphire substrate is defined as a light extraction surface, and the other surface of the sapphire substrate is defined as a device formation surface on which the InGaN semiconductor light emitting portion is provided. The InGaN semiconductor light emitting portion includes an InGaN active layer sandwiched between an N-type GaN contact layer and a P-type GaN contact layer. For example, the N-type GaN contact layer is disposed adjacent to the sapphire substrate, while the P-type GaN contact layer is disposed adjacent to the mounting board. In this case, a P-side electrode film is provided on a surface of the P-type GaN contact layer. An N-type electrode film is provided on a portion of the N-type GaN contact layer exposed by removing parts of the P-type GaN contact layer and the InGaN active layer.
Further, a P-side pad electrode and an N-side pad electrode are respectively connected to the P-side electrode film and the N-side electrode film. These pad electrodes are bonded to the mounting board in opposed relation, thereby achieving flip-chip bonding of the light emitting diode.
Not all the light emitted from the InGaN semiconductor light emitting portion is extracted through the sapphire substrate, but the light is partly directed toward the P-type GaN contact layer. In order to increase the light extraction efficiency, the P-side electrode film should be composed of a material which not only provides ohmic contact with the P-type GaN contact layer but also has a sufficient reflectivity. This imposes heavy restrictions on device production, making it difficult to form a P-side electrode film having a smaller contact resistance and a higher reflectivity.    Patent Document 1: Japanese Patent Publication No.    Patent Document 2: Japanese Unexamined Patent Publication No. 2003-224297